LIKE ITS imitator, the computer, the human brain runs on electricity, and like any electrical appliance, the brain emits small magnetic fields as it operates.
Scientists are on the verge of using that simple fact of physics to unlock secrets of the brain that range from diagnosing illnesses to mapping the origins of our thoughts.
This is possible through use of a machine that can detect the weak magnetic fields produced by brain cells and distinguish them from the many other fields around us, such as those emitted by elevators, radio sets, traffic lights and the Earth itself.
The machine, called a magnetoencephalograph, uses detection coils that are cooled by liquid helium to ultracold temperatures in which most electrons in the coils are in the same energy state, making them extremely sensitive to small changes in magnetic fields.
By appropriately designing the geometry of these coils, physicists have found a way to cancel out most steady-state or ”background” magnetic fields such as that of the Earth, making the coils exquisitely sensitive to very feeble magnetic fields that are extremely close.
Because magnetic fields pass through brain tissue and the skull without distortion, their detection offers scientists their best chance yet for a window into the workings of the brain.
Early use of magnetoencephalography, or MEG, has already provided psychologists with significant information about the origin of certain types of thought and has pinpointed brain lesions causing epileptic seizures, letting surgeons know where to cut to end the seizures.
This has been accomplished using prototype equipment with one or a few sensor coils that require several readings from different locations on the scalp to derive useful information. This summer, the first MEG machine containing 14 sensor coils will be installed at the New York University Medical Center on Manhattan`s East Side, and physicians will begin in earnest to explore just how useful the technique may be.
In a few years, an MEG machine with 100 sensor coils should be ready for use.
This will be a supercooled device attached to a helmet, resembling a hair dryer taken from the neighborhood beauty salon and converted to a high-tech detector of magnetic fields. The information will be fed into computers and presented on video screens in much the same way that images derived from X-rays are produced by computerized tomography (CT) equipment.
Unlike a CT scan, the MEG is totally passive. It emits no radiation and requires the patient to do nothing more than sit with his head inside the detector bowl and think.
Stimulation of the subject under study is totally harmless and may consist of flashing lights at the subject, rubbing a feather over a finger or squirting water in an ear.
”This will provide faster, more accurate and less invasive testing for patients. It is what people expect of modern technology in medicine,” said Dr. Rodolfo Llinas, chairman of biophysics and physiology at the NYU Medical Center.
MEG machines with 14 or more magnetic field detectors allow physicians to look at a portion of the brain and monitor its function in real time, Llinas said. That means that brain functions can be monitored a fraction of a second after they occur.
MEG gives a different look at the same kind of information gathered from electroencephalography, or EEG, the technology that uses recording electrodes pasted to the scalp to pick up electrical signals from groups of nerve cells. These electrical signals are distorted as they pass through the skull to the scalp, unlike magnetic fields, which aren`t affected by soft tissue or bone.
Using MEG and EEG together would greatly enhance the physician`s knowledge of brain function, Llinas said.
”It is like taking information about the universe received from a radio telescope and combining it with information from an optical telescope,”
Llinas said. ”All the information is complementary.”
An example of how MEG information may complement existing knowledge about the brain has already occurred at the NYU psychology and physics departments, where prototype machines have been used for several years to study brain waves.
A particular kind of electrical brain wave pattern called P300 by psychologists has been studied for years. This is sometimes called the
”oddball wave” because it occurs when a subject has an unfulfilled expectation.
If someone is shown several pictures of the same scene, for example, but then one picture has a variation, the P300 wave may occur. It probably indicates a thought that updates our expected perceptions, causing us to rethink a situation, as when driving home over a familiar route one suddenly discovers that construction work has closed a street.
Working with magnetic field detection, Lloyd Kaufman, Sam Williamson and Yoshio Okada, NYU researchers, have found the P300 wave originates in a portion of the hippocampus, a swelling in the floor of the lateral ventricle of the brain. Pinpointing the origin of the much-studied P300 wave so precisely wasn`t possible with EEG studies alone.
In other studies, NYU researchers have shown the origin of the thought when a person begins to move his finger, and that the origin shifts slightly immediately after movement begins, presumably because of a feedback mechanism used by the brain to monitor body movements.
Physicists first started supercooling metals because they wanted to study the quantum properties of materials with a large number of electrons placed in the same energy state, said Williamson, a physicist.
”People did it just because it tickled them to watch the wave effects,” he said.
Monitoring magnetic fields in the brain became a realistic goal after NYU researchers determined how a series of supercooled coils could be positioned so as to cancel out effects of large, uniform magnetic fields.
By determining where in the brain certain functions originate, it may be possible to diagnose a number of diseases that are often misdiagnosed with current techniques. By using MEG, for example, schizophrenia may be distinguished from other mental illnesses that share the same symptoms.
Alzheimer`s disease may be distinguished from other forms of dementia, Williamson said.
At the UCLA, Dr. William Suthering, a neurologist, and Dr. Daniel Barth, a neuroscientist, have used MEG to determine the origin of epilepsy. The standard technique for doing this requires opening the skull and implanting electrodes directly into the brain.
At the University of Rome, researchers have used MEG to discover pathologies in brain function and pinpoint lesions in the brain too small to be seen with CT X-ray scans or other modern imaging techniques.
Llinas said that once a database of information on MEG brain studies is built, ”it could redefine a whole range of illnesses. We`ll be seeing things we`ve never seen before.”
Llinas envisions a national computer-linked network of MEG users that will greatly benefit people who have rare neurologic diseases.
”There might be only 25 people in the country with a given condition,”
he said, ”but through this network, their physicians could recognize that they had the same pathology. Information on treatments and reactions to treatment could be shared.”
MEG offers new insights into diagnosing and treating patients who suffer from dizziness, migraine headaches, ringing in the ears, intractable pain and numerous other problems of the central nervous system, Llinas said.
The technique should prove inexpensive enough and easy enough to use so that most community hospitals will have MEG machines within five years, he said. Larger, more expensive and complex machines may be limited to major medical centers for sophisticated diagnosis and research, but smaller machines may become a vital part of every well-equipped emergency room.
”I can see the day when this test would be required for every patient who comes into the hospital unconscious,” Llinas said.
NYU is collaborating in a three-year study of MEG with Biomagnetic Technologies Inc., a San Diego-based firm that has built and will service GEMINI, the state-of-the-art MEG machine to be installed at NYU in July.
The brain isn`t the only organ to use electrical charges and emit magnetic fields as it functions. The heart, liver and all other major organs do the same. Some MEG work has already been directed at liver function, and as more is learned about MEG use, it is likely that knowledge about all parts of the body will be enhanced through this new technique, researchers predict.
